It's essential to prepare some error handling stuff. Our app will produce errors and the user is fool (we must assume that 👶 )
Backend
Prepare the error_handler @ traintool/src/app.yaml
Frontend
Prepare the error4**/5** .html files to be showed by the handler.
Backend
Prepare the error_handler @
traintool/src/app.yamlFrontend
Prepare the error4**/5**
.htmlfiles to be showed by the handler.